A commonly used circuit board terminal is a socket connector pin that includes an upper portion in the form of a sleeve that holds a spring contact which clips to component leads as they are inserted, and a lower portion to which wires are terminated. Such pins are provided with a variety of wire terminations, including Stitch-wire terminations, Wire-wrap terminations (of three common tail lengths), and insulation displacement terminations. One type of wire termination is Solder-wrap, which commonly does not use a connector pin although greater reliability could be achieved if a machined pin were used.
The sleeve portions of prior socket pins have had blind holes which were electroplated to receive plated contact clips. Plating chemicals tend to become trapped at the bottom of the blind hole, which can lead to corrosion problems which are virtually undetectable immediately after assembly but which can later cause major reliability problems. Some manufactureres have drilled vent holes through the side of the sleeve portion to aid in rinsing of plating solutions, but the crossdrilling weakens the pin and adds to its cost. It would be desirable if a concentric through hole could be used instead of a blind hole, but the wire termination has been in the way.
Stitched bonding, used for high reliability applications, requires the wire termination (bonding surface) to be formed of stainless steel to facilitate diffusion bonding of nickel wires thereto. However, stainless steel alloys are extremely tough and slow to machine, and when type 303 series stainless steel is used for at least minimal machinability, sulfur and lead are added. These elements are disastrous for fusion welding and detrimental to diffusion bonding (stitch-bonding). The use of sulfur and lead causes a need for process adjustments which complicate in-process controls and increase costs. Another problem with stitch bonding terminations is that in circuit board designs with small holes, the diameter of the Stitch-wire surface which can pass through the hole is very small to accommodate printed circuit traces in between pins. As a result, the bonding of two wires to one small diameter pin is very difficult. It would be of considerable value if Stitch-wire socket pins were available which could be constructed at low cost with desirable stainless steel bonding surfaces and which could have large bond areas. It may be noted that "back loaded" stitch wire pins with large bond areas have been used that are installed from the bottom, or wiring side of the board; however, this has disadvantages including a very narrow entry for component leads and a narrow upper shoulder. These pins must also be mounted in 0.065" diameter or larger holes instead of the more common 0.055" diameter holes.
Insulation displacement socket pins have previously been designed for mounting in 0.065 inch diameter holes to enable the socket pin to be mounted from the wiring side of the circuit board. However, socket pins for other wiring processes have generally been mounted in 0.055 inch diameter holes, which cannot accept the insulation displacement pins. It would be desirable if the prior art style insulation displacement terminals were available which could mount in the smaller holes, allowing common circuit board designs to be utilized for any one of the wiring processes.
The tails of wire-wrapped pins are preferrably of cold-formed, spring tempered phospher bronze or beryllium cooper so they are rigid and of uniform shape and surface finish. However, the rest of the pin is most easily made on automatic screw machines (a type of lathe), where free machining brass is highly desirable. Prior art pins had tails machined of brass and then cross-milled to form a 0.025 inch square post, which resulted in inconsistant cross-sectional shapes and rough surface finishes. It would be desirable if the ideal material and forming processes were usable with each portion of the pin.
Circuit board pins are often formed with a barb or a straight spline to hold them in place. The barbs provide good retention, but tend to stress the circuit board unevenly to cause warping and may not be reliable in resisting turning during wire wrapping. The spline resists turning, but is not as good as a barb for retention in the board. A retention system which was highly effective and which minimized uneven stressing of the circuit board would be desirable.
A circuit board system which enabled almost complete assembly, with any of a variety of separate terminations readily added at a later time, would enable rapid supply of custom board assemblies.